Related Clues:

• Sirens
• Cautionary signals
• Trading updates
• Uses a cell phone, maybe
• School books
• Contacts via cell phone, in a way
• Cautions
• Gives a heads up
• Contacts by phone, in a way
• Backpack fillers
• Red lights and flares
• College bookstore stock
• Foghorn blasts, e.g.
• Notifies
• Beeps, maybe